<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        @media screen and (max-width:420px) {
            html {
                font-size: 20px;
            }
        }
        
        @media screen and (min-width:600px) {
            html {
                font-size: 40px;
            }
        }
        
        @media screen and (min-width:1000px) {
            html {
                font-size: 100px;
            }
        }
    </style>
</head>

<body>
    <div>123321</div>
</body>

</html>